Acetyl exchange between acetyl chloride and sterically hindered aryl ketones under Friedel–Crafts conditions

Abstract

The kinetics of acetyl exchange between acetylmesitylene, or acetyldurene, and ¹⁴C-labelled acetyl chloride have been measured in nitromethane solution in the presence of aluminium chloride. Mechanistic studies using acetyl[3,5-²H₂]mesitylene as substrate show conclusively that acetyl exchange proceeds, not by acylation–deacylation or deacylation–acylation, but via a synchronous reaction involving an ipso-complex. Theoretical calculations (MNDO) indicate that of three possible synchronous pathways, two are energetically feasible.